surface: Deleted duplicate ammo member variable of Launcher.

The super class ArmBase already had that variable.  The variable name is
overridden (hidden) so apparently it works, but it would cause problems
when it comes to serialization.
surface: Change the way to store script controlled values for Aerial.

In aerialLanding.nut, we have been used a global table with Entity IDs
as indices to store script relevant parameters for each object.
It has been worked, but has a problem that garbage entries will remain
in the table after deleting an associated object.  Adding delete hook to
clear the table would be a way, but we'd like to take more direct solution;
Aerial instance has an arbitrary Squirrel object as its parameter.
This method is proven to work in HellfireProc().
surface: Revive means to reload aerialLanding logic on the fly.

Before aerialLanding.nut was renamed from aerial.nut, we had been able
to reload the script by "aerial" console command while the game is running.
This functionality is disabled since rename, but now available again.